The invention is based on a method and a control device for the procedure of burning off deposits from a hot wire in a constant-temperature anemometer, and further including a switching device for increasing the current through the hot wire relatively briefly in accordance with operating characteristics. An air flow rate meter operating on the principle of a constant-temperature anemometer is known from German Offenlegungsschrift No. 17 50 050, the hot wire of which is burned off after each measurement cycle in order to clean it. This is effected in the known device by means of a severe bridge imbalance and the high current flow caused thereby. Such burnoff procedures put a heavy load on the hot wire. In order to reduce this load, it has already been proposed to reduce the number of burnoff procedures, so that burnoff is performed not after each measurement cycle but only after a certain number of measurement cycles, for instance. Although these known devices do produce satisfactory results as a rule, still certain problems still arise during the course of actual operation.
The burnoff of deposits on hot wires is effected at temperatures of 1050.degree. C., for example. The burnoff procedure lasts approximately 1 second. If the procedure is initiated after a measurement cycle has ended, that is, when the engine has stopped, then if the engine is still at operational temperature this may cause the ignition of fumes rising from the intake tube. The result is an uncontrolled temperature increase at the hot wire, which may in turn cause the destruction of the hot wire.